Formation of durable protective coatings have been found to be of great importance in the glass container industry to minimize unsightly scratch and scuff marks, and to minimize glass breakage of newly formed glass articles, or ware, by protecting the articles against contact abrasion damage. Uncoated glass articles are highly susceptible to abrasion damage, and it has been reported that newly formed uncoated glass articles can quickly lose up to 75% of their bursting strength due, at least in part, to surface abrasion caused by contact with other glass articles, as normally occurs during processing and handling of such articles.
While some coatings have been applied to articles just prior to use, the articles are usually coated soon after they are formed, and in the case of annealed articles, for example, such coatings have been applied immediately before and/or after annealing.
Typically, pre-annealing coatings, sometimes referred to as "hot end" coatings, are applied to glassware in an initial coater after it leaves the glassware machine. The initial coater forms a very thin metal oxide coating on the outer surface on the surface of the glassware, which is then carried to the annealing lehr. Commonly used metal oxides include tin compounds and titanium oxide. Such pre-annealing coating methods and apparatus are disclosed for example, in U.S. Pat. Nos. 2,710,267; 2,831,780; 3,004,863; 3,051,593; 3,130,071; 3,684,469; 4,431,692; 4,457,957; 4,615,916; 4,668,268; 4,719,126; and 4,719,127.
A number of post-annealing coatings, sometimes referred to as "cold end" coatings, and methods and apparatus for their application, have been disclosed, for example, in U.S. Pat. Nos. 2,995,633; 3,386,855; 3,387,994; 3,487,035; 3,712,829; 3,801,361; 3,876,410; 3,989,004; 3,997,693; 4,039,310; 4,130,407; 4,135,014; 4,517,242; 4,517,243; 4,529,657; and 4,812,332.
Electrostatic deposition methods and apparatus are well known. Such methods and apparatus have been in common use in industry to apply various useful, protective and decorative coatings. Examples of such electrostatic coating methods and apparatus include U.S. Pat. Nos. 2,685,536; 2,794,417; 2,893,893; 2,893,894; Re. 24,602; 3,048,498; 3,169,882; 3,169,883; 3,323,934; 3,645,778; 3,991,710; 4,073,966; 4,170,193 and many others. Notwithstanding their extensive development and use, electrostatic coating methods and apparatus have not been used to apply a metal oxide vapor to a surface of hot glass to form a metal oxide coating as either a hot end coating or as a cold end coating.
Among the above-identified patents, U.S. Pat. Nos. 4,039,310 and 4,130,407 disclose methods of strengthening glass against failure. U.S. Pat. No. 4,039,310 discloses a method of strengthening glass by heating the glass to a temperature in excess of 700.degree. F. (371.degree. C.) but below the decomposition temperature of a selected fatty acid, such as behenic, stearic or glutamoric acid and applying the fatty acid to the heated glass. U.S. Pat. No. 4,130,407 discloses a method of strengthening glass by applying a fatty acid derivative of an inorganic salt at temperatures between 100.degree. C. (212.degree. F.) and 500.degree. C. (932.degree. F.).
U.S. Pat. No. 2,831,780 discloses a method for increasing the scratch resistance of a glass surface by treating the surface while at a temperature between the strain temperature and the deformation temperature of the glass, such as between 450.degree. C. to 600.degree. C. (778.degree. F. to 1048.degree. F.), with a vapor of a metallo-organic ester selected from a group consisting of alkyl titanate, alkyl zirconates, alkyl aluminates, and mixtures thereof which pyrolyzes to form a metal oxide coating on the glass surface. Specific examples of such metallo-organic esters include aluminum ethoxide, aluminum isopropoxide, tetra-isopropyl titanate and tetra-t-butyl zirconate.
U.S. Pat. No. 3,684,469 discloses a method of hot end coating predetermined areas of glassware by moving the glassware between closely spaced coacting dispensing nozzles and exhaust ports which cooperate together to distribute the coating, such as a fog or an aerosol of titanate material, across the barrel of the glassware without coating the finish of the glassware.
U.S. Pat. No. 4,457,957 discloses a method for applying an inorganic titanium containing coating to a glass surface by contacting the surface at an elevated temperature with a thermally decomposable tetraalkyl titanate applied to the glass surface as a mixture in a non-aqueous, normally-liquid vehicle selected from a group consisting of normally-liquid esters of fatty acids and silicon fluids.
U.S. Pat. No. 4,615,916 discloses a method for forming a metal oxide coating on the exterior of glass containers moving through a treatment zone in which the treatment zone utilizes heated compressed air aspirators to cause a vapor laden air contained in chambers to be propelled across the width of the ware conveyor from both sides at adjacent, horizontally spaced, points in the conveyor length.
U.S. Pat. Nos. 3,876,410 and 3,989,004 disclose the use of a coating material that is, at least in part, vaporizable at a readily obtainable temperature and capable of producing vapor that is contact-adherent to the article to be coated to produce a durable and tenacious, lubricous coating. In general, the patents disclose that an acceptable coating material can be formed from organic materials, particularly hydrocarbons formed from methylene, ethylene, propylene, butylene, fatty acids and their derivatives and the like, and that to be particularly effective, the vapor molecules of the coating material should be of a polar-non-polar nature such that the polar portion of the molecule will tend to adhere strongly to the article to be coated and oriented so that the non-polar portion of the molecule forms the lubricous external surface. Caporic acid, stearic acid, oleic acid, myristic acid, linolic acid and palmatoleic acid are disclosed as typical of the compositions yielding desirable coatings on glassware when used according to the method of the above patents.
Notwithstanding the disclosures of the above-identified patents, a need exists in the manufacture of coated glass containers for method and apparatus for forming an inexpensive, thin, tenacious and protective coating on glassware by electrostatically applying a metallic vapor either as a hot end coating or as a cold end coating, and either as a single coating or as a part of a dual coating process.